The present invention relates to a multi-chip-module (MCM) type semiconductor device.
JP-A-11-220077 discloses that a thermal expansion coefficient of a substrate is adjusted to restrain a crack of a semiconductor element or a under-fill layer. JP-A-2000-40775 discloses that a shape of an oblique surface of the under-fill layer is adjusted to restrain the crack of the semiconductor element. JP-A-6-244238 discloses that the semiconductor elements are mounted one by one onto a substrate sequentially in order of semiconductor element thickness from a minimum semiconductor element thickness.
An object of the present invention is to provide a multi-chip-module (MCM) type semiconductor device of high-reliability against a bending deformation of the MCM type semiconductor device caused by an environment temperature variation during actual operation thereof, a mounting treatment of semiconductor element onto a substrate, a heat generation thereof during actual operation thereof or the like, with a difference in linear expansion coefficient between the semiconductor element and a substrate, a difference in temperature therebetween, an external force applied to the semiconductor device.
According to the invention, a multi-chip-module type semiconductor device comprises, first and second semiconductor elements, a main component of each of the semiconductor elements being semiconductor material to form a semiconductor electric circuit in each of the semiconductor elements, and a substrate adapted to be mounted onto a mother board and to be electrically connected to the mother board, on which substrate the first and second semiconductor elements are mounted to be electrically connected to the substrate, so that the first and second semiconductor elements are electrically connected to the mother board through the substrate.
If a thickness of the second semiconductor element is less than a thickness of the first semiconductor element when an area of the second semiconductor element is more than an area of the first semiconductor element as seen in a stacking direction in which each of the first and second semiconductor elements and the substrate are stacked and/or a length of a side of the second semiconductor element whose length is maximum in comparison with lengths of the other sides of the second semiconductor element as seen in the stacking direction is more than a length of a side of the first semiconductor element whose length is maximum in comparison with lengths of the other sides of the first semiconductor element as seen in the stacking direction, since a stress on a connecting member (for example, bumps) between the substrate and each of the semiconductor elements increases in accordance with an increase of the area and/or the length of the side whose length is maximum in comparison with lengths of the other sides while the stress on the connecting member (for example, bumps) between the substrate and each of the semiconductor elements decreases in accordance with a decrease of the thickness of each of the semiconductor elements, a crack on the connecting point or separation between the semiconductor element and the substrate at the connecting point is effectively prevented by decreasing the thickness of the second semiconductor element. It is preferable for the thickness of each of all semiconductor elements on the substrate to be not more than 0.4 mm.
The multi-chip-module type semiconductor device may further comprise a synthetic resin (corresponding to an under-fill) adhering to the substrate and each of the first and second semiconductor elements, and/or a wiring layer between the substrate and at least one of the first and second semiconductor elements, the wiring layer including a synthetic resin layer and an electrically conductive member (connecting electrically therethrough the substrate to the at least one of the first and second semiconductor elements) extending in a transverse direction transversing the stacking direction, in such a manner that an electrical connecting point between the semiconductor element and the electrically conductive member is distant away from an electrical connecting point between the electrically conductive member and the substrate in the transverse direction. When each of the first and second semiconductor elements includes a first surface facing to the substrate and a second surface as a reverse surface with respect to the first surface in a stacking direction in which each of the first and second semiconductor elements and the substrate are stacked, and the thickness of the second semiconductor element is smaller than the thickness of the first semiconductor element, it is preferable that the second surface of the first semiconductor element is prevented from being a grinder-finished surface while the second surface of the second semiconductor element is the grinder-finished surface.
If the thickness of the first semiconductor element is smaller than the thickness of the second semiconductor element when the multi-chip-module type semiconductor device further comprises a synthetic resin member (corresponding to the under-fill) adhering to the first semiconductor element and the substrate at the inside of the first semiconductor element as seen in the stacking direction, while a synthetic resin (for example, corresponding to the under-fill) whose Young""s modulus is not less than Young""s modulus of the synthetic resin member is prevented from adhering to the second semiconductor element and the substrate at the inside of the second semiconductor element as seen in the stacking direction, since a connecting rigidity between the first semiconductor element and the substrate connected to each other through bumps is made more than a connecting rigidity between the second semiconductor element and the substrate connected to each other through bumps, by reinforcing the connecting rigidity between the first semiconductor element and the substrate with the synthetic resin member, the stress on the semiconductor element increases in accordance with an increase of the connecting rigidity between the semiconductor element and the substrate, and the stress on the semiconductor element decreases in accordance with the decrease the thickness thereof on the substrate, the crack or excessive stress on the first semiconductor element whose connecting rigidity is reinforced by the synthetic resin member is effectively prevented.
If the thickness of the first semiconductor element is smaller than the thickness of the second semiconductor element when the multi-chip-module type semiconductor device further comprises a first synthetic resin through which the substrate and the first semiconductor element are connected to each other and a second synthetic resin through which the substrate and the second semiconductor element are connected to each other, and Young""s modulus of the first synthetic resin (for example, corresponding to the under-fill) is larger than Young""s modulus of the second synthetic resin (for example, corresponding to an elastomer stress or deformation absorbing layer 13), since the connecting rigidity between the first semiconductor element and the substrate connected to each other through bumps is made more than the connecting rigidity between the second semiconductor element and the substrate connected to each other through bumps, by relatively more effectively reinforcing the connecting rigidity between the first semiconductor element and the substrate with a difference in Young""s modulus between the first synthetic resin and the second synthetic resin, the stress on the semiconductor element increases in accordance with the increase of the connecting rigidity between the semiconductor element and the substrate, and the stress on the semiconductor element decreases in accordance with the decrease of the thickness thereof on the substrate, the crack or excessive stress on the first semiconductor element whose connecting rigidity is reinforced relatively more effectively by the difference in Young""s modulus between the first synthetic resin and the second synthetic resin is effectively prevented.
If the thickness of the first semiconductor element is smaller than the thickness of the second semiconductor element when the multi-chip-module type semiconductor device further comprises the first synthetic resin (for example, corresponding to the under-fill) adhering to the substrate and the first semiconductor element at the inside of the first semiconductor element as seen in the stacking direction, and a second synthetic resin (for example, corresponding to the sealing resin 10 and/or support plate 12) through which the second semiconductor element is connected to the substrate at the outside of the second semiconductor element as seen in the stacking direction while a synthetic resin (for example, corresponding to the under-fill) whose Young""s modulus is not less than Young""s modulus of the first synthetic resin is prevented from adhering to the second semiconductor element and the substrate at the inside of the second semiconductor element as seen in the stacking direction, since the connecting rigidity between the first semiconductor element and the substrate connected to each other through bumps with the first synthetic resin (for example, corresponding to the under-fill) adhering to the substrate and the first semiconductor element at the inside of the first semiconductor element as seen in the stacking direction is made more than the connecting rigidity between the second semiconductor element and the substrate through the second synthetic resin at the outside of the second semiconductor element as seen in the stacking direction without the synthetic resin whose Young""s modulus is not less than Young""s modulus of the first synthetic resin at the inside of the second semiconductor element as seen in the stacking direction so that the connecting rigidity between the second semiconductor element and the substrate is substantially formed by a bending low rigidity of the second synthetic resin, the stress on the semiconductor element increases in accordance with the increase of the connecting rigidity between the semiconductor element and the substrate, and the stress on the semiconductor element decreases in accordance with the decrease of the thickness thereof on the substrate, the crack or excessive stress on the first semiconductor element whose connecting rigidity is made more than the connecting rigidity between the second semiconductor element and the substrate is effectively prevented.
If the thickness of the second semiconductor element is smaller than the thickness of the first semiconductor element when a main component of the first semiconductor element is Si, a main component of the second semiconductor element is GaAs, since Young""s modulus of GaAs is more than Young""s modulus of Si, a rigidity against bending of the semiconductor element increases in accordance with an increase in Young""s modulus of the semiconductor element, the stress on the semiconductor element increases in accordance with an increase of the rigidity against bending of the semiconductor element, and the stress on the semiconductor element decreases in accordance with the decrease in thickness thereof on the substrate, the crack or excessive stress on the second semiconductor element whose rigidity against bending is made more than the rigidity against bending of the first semiconductor element by a difference in Young""s modulus between the first and second semiconductor elements is effectively prevented.
When each of the first and second semiconductor elements includes a first surface facing to the substrate and a second surface as a reverse surface with respect to the first surface in the stacking direction, and the second surface of the first semiconductor element is prevented from being a grinder-finished surface while the second surface of the second semiconductor element is the grinder-finished surface, an efficiency in heat discharge from each of the semiconductor elements can be adjusted desirably, because the efficiency in heat discharge from the semiconductor element changes in accordance with a thickness between the second surface and the electric circuit which is formed or treated from the first surface and the thickness between the second surface and the electric circuit can be adjusted by the grinder-finishing.
If a thickness of the second semiconductor element is less than a thickness of the first semiconductor element when an area of the second semiconductor element is less than an area of the first semiconductor element as seen in the stacking direction in which each of the first and second semiconductor elements and the substrate are stacked and/or a length of a side of the second semiconductor element whose length is minimum in comparison with lengths of the other sides of the second semiconductor element as seen in the stacking direction is less than a length of a side of the first semiconductor element whose length is minimum in comparison with lengths of the other sides of the first semiconductor element as seen in the stacking direction, since a stress on a side surface of each of the semiconductor elements (particularly, a connecting point between the side surface and a terminating end of an exposed surface of an under-fill adhering to the substrate and the semiconductor element) increases in accordance with a decrease of the area and/or the length of the side whose length is minimum in comparison with lengths of the other sides as shown in FIG. 9 (a possibility of crack occurrence on the second semiconductor element is more than that on the first semiconductor element when the thickness of the second semiconductor element is substantially equal to that of the first semiconductor element), it is difficult for the side surface to be correctly formed through dicing process for dividing a semiconductor wafer to the semiconductor elements sufficiently for securely preventing a stress concentration on the side surface, and the stress on the semiconductor element decreases in accordance with a decrease of the thickness thereof on the substrate, the crack on the side surface of the second semiconductor element is effectively prevented by decreasing the thickness of the second semiconductor element without excessive treatment of the side surface of the second semiconductor element.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.